1. Field of the Invention
The present invention relates to a lens barrel which is provided with barrier blades disposed in the front of a photographic optical system, for protecting a photographic lens and openably covering an image-taking.
2. Description of the Related Art
A conventional lens barrel of the above-mentioned type is disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H07-159856.
The lens barrel is provided with a pair of barrier blades for openably covering an image-taking formed in the front of a photographic optical system, and the barrier blades are opened and closed by a barrier drive ring that rotates about the optical axis. A rotational force of a rotational barrel is transmitted to the barrier drive ring via a connecting shaft.
A barrier-closing spring is mounted between each of the barrier blades and the barrier drive ring. The barrier-closing spring always holds the associated barrier blade in contact with the barrier drive ring in a manner urging the barrier blade in the closing direction to thereby accommodate or absorb the motion of the barrier drive ring in a direction away from the barrier blades.
Further, between the barrier drive ring and a lens barrel cover, there is mounted a barrier-opening spring that urges the barrier drive ring to drive each of the barrier blades in the opening direction.
When the rotational barrel rotates in one direction, the rotational force of the rotational barrel is transmitted to the barrier drive ring via the connecting shaft, and the barrier drive ring rotates in the one direction while charging the barrier-opening spring.
At this time, each of the barrier blades is pressed by the associated barrier-closing spring to turn in the other direction according to the rotation of the barrier drive ring. As a consequence, the barrier blades are closed to cover the image-taking in the front of the photographic optical system.
On the other hand, when the rotational barrel rotates in the other direction, the rotational barrel is unhooked from the connecting shaft, and the barrier drive ring is rotated in the other direction by the charged spring force of the barrier-opening spring.
At this time, the barrier blades turn in the other direction according to the rotation of the barrier drive ring. As a consequence, the barrier blades are opened to open the image-taking in the front of the photographic optical system. Then, when fully opened, the barrier blades come into abutment with respective stoppers, whereby the pivotal motion of each of the barrier blades is restrained to stop the rotation of the barrier drive ring.
By the way, in recent years, for reduction of the size or thickness of cameras, the reduction of the size of the lens barrel is demanded. However, it is conventionally required to dispose the barrier blades on the front side of components of the lens barrel or on the inner side of the same, so as to prevent the component parts from interfering with the barrier blades when the lens barrel is collapsed. This makes it necessary to provide accommodation spaces for the barrier blades, and hence it is difficult to reduce the size or thickness of the lens barrel.
As a solution to this problem, there has been proposed a lens barrel in which two barrier blades are caused to perform an opening operation in the same direction, so as to be received in a blade accommodation section formed in a portion of the lens barrel around the opening thereof, whereby a space for accommodating some or part of components of the lens barrel is formed on a side opposite to a side where the blade accommodation section is disposed, with respect to the optical axis (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 06-67261).
According to the proposal, it is stated that when the lens barrel is collapsed, by accommodating some or part of components of the lens barrel in the accommodation space on the side opposite to the side where the blade accommodation section for the barrier blades is disposed with respect to the optical axis, it is possible to make effective use of the accommodation space conventionally used for accommodating one of the barrier blades, and thereby attain reduction of the length of the lens barrel.
According to Japanese Laid-Open Patent Publication (Kokai) No. 06-67261, however, the space for accommodating the components of the lens barrel can only be formed on the side opposite to the side where the blade accommodation section for the barrier blades is disposed with respect to the optical axis. Further, since the two barrier blades are received in an overlapping manner when they are opened, the thickness of the blade accommodation section increases in the direction of the optical axis, which increases the collapsed lens barrel length.